Card sharing countermeasures

A method for identifying of at least an identifier of a conditional access card used in a control word redistribution system by passing information over a side channel, said method comprising a modification step of a response time, of the card, to a control word request, according to a predefined function which depends on the identifier of the said cards, the said modification step coding the identifier of the card within response times of this card to control word requests by inserting or not inserting, according to the predefined function, a time delay offset before the card answer to a control word request so that the said identifier may be recovered through correlation measures between measured response time signatures of the card and expected response time signatures.